Add a new Generate SourceKit-LSP Configuration command

[award999]

Description

• Add a new command that will generate the .sourcekit-lsp/config.json file for one or all the folders in the workspace
• Separate the select folder quick pick used to generate launch configurations so it could be reused
• Add configurationBranch setting so the user can hardcode
• Add a jsonValidation contribution to the manifest, the $schema property added by command takes precedence
• We'll always fall back to "main" if the expected branch does not exist
• Add new logic where if "-dev" suffix in version, we assume it is a "main" build

Note in a follow up PR I'm going to add logic to watch this file and prompt them to update the schema if the toolchain version changes

Issue: #1208

Tasks

• Required tests have been written
• Documentation has been updated
• Added an entry to CHANGELOG.md if applicable